Thermostat switch



Dec. 15, 1931. J, BURT THERMOSTAT SWITCH Original Filed Jan. 8, 1929INVENTOR E. C]. .BLLlt ATTORNEY Patented Dec. 15, 1931 UNITED STATESPATENT OFFICE ELMER J. BURT, F OAKLAND, CALIFORNIA, ASSIGNOR TOTHEBMOSTOVE CORPORATION, LTD., 0F RENO, NEVADA, ACORPORATION OF NEVADA'rnnmvrosrer swrron Application filed January 28, 1929, Serial No.335,403. Renewed May 22, 1931.

This invention relates to electric switches and particularly to one foruse in connection with electric thermostoves, in which it is desired todiscontinue the operation of the electric heating element after the foodbeing cooked has reached the boiling temperature and is throwing offsteam.

The principal object 'of my invention is to provide a switch for thispurpose which is operated by steam heat in such a manner that thecircuit will be opened when such heat has been attained in a positiveand automatic manner. The switch arrangement also is such that it may beeither closed or opened at will, independently of the automatic switchopening structure but incapable of functioning to close the switch untilthe heat in the stove has dropped to at least below the boiling point.

A further object of the invention is to produce a simple and inexpensivedevice and yet one which will be exceedingly effective for the purposefor which it is designed.

These objects I accomplish by means of such structure and relativearrangement of parts as will fully appear by a perusal of the followingspecification and claims.

In the drawings similar characters of reference indicate correspondingparts in the several views:

Fig. 1 is a side elevation of my improved switch showing the contactsclosed.

Fig. 2 is a similar view with the contacts open.

Fig. 3 is a top plan view of the steam passage unit of the switch partlyin section and showing the same mounted in connection with the stove.

Fig. i is a perspective view of a pawl member, detached. I I

Referring now more particularly to the characters of reference on thedrawings, the numeral 1 denotes a box or casing of porcelain or similarinsulating material adapted to be disposed on' the side of the stove onthe outside thereof. The box is held in this position by a threaded stem2 projecting through the back of the box at one end and through thedouble walls 3 of the stove, to which walls the stem is clamped bysuitable nuts 4. A

block 5 is secured to the inner end of the stem inside the box, to whichblock is secured an 1 aluminum pipe 6 which extends horizontally to theopposite end of the box and is freely open to the atmosphere at suchend.

The stem has a passage 7 from its end inside the stove to a terminationinside the block and communicating at such end with the adjacent end ofthe pipe 6 as shown in Fig. 8. V

Mounted in. the box is a fixed contact 8 to which is connected a wire 9leading to one terminal of the stove heating element (not shown).Positioned above the contact 8 tocooperate therewith is another contact10 Which is connected to one end of a horizontally extending flat springarm 11 which is pivoted intermediate its ends onto the back wall of thebox. A spring 12 acts on the arm to normally hold the contactsseparated. The contact 10 is connected to a flexible wire 13 leading toa connection with a plug stem 14 projecting outwardly from the end ofthe box; the corresponding stem 15 being connected by a wire 16 to theother terminal of the element.

Pivoted in the box toward the end thereof opposite the contacts andpositioned to projectunder the adjacent end of the arm 11 is a verticalpawl 17 which when under the arm depresses the opposite end of the sameagainst the action of the spring 12 so that the contacts will firmlyengage each other to close the circuit. A spring 18 associated with thepawl tends to turn the same toward an engaging position with the arm.

Formed as a part of the pawl in offset relation to the pivot thereof andin the direction of the contacts is a transversely projecting extension19 which passes over a flat strip 20 of bimetal which extends along andnormally rests on the pipe 6. This strip is free at its extensionengaged end but'is permanently secured at its opposite end on the block5. This bimetal strip is so disposed that its expansible portion isunderneath, so that when affected by heat it will curl upwardly at itsfree end.

By means of this construction therefore it will be seen that when steamis generated in the cooker and is passing through the steam and pipeheating the same, the heat will be transmitted to the bimetal strip,causing the latter to assume the above named warped position. If thepawl has been previously turned so as to be engaged with the arm 11and'the switch is therefore closed, the extension 19 will be depressedand will bear firmly on the bimetal strip. As the latter warps up, itraises the extension, causing the pawl'to be thrown clear of the arm 11against the resistance of the spring 18, the strength of said springbeing insuiiicient to resist the warping movement of the bimetal strip.The spring 12 then acts on the arm 11 to raise the contact 10 clear ofthe contact 8, opening the switch. The switch will not then again close,even with the return of the strip to its normal position, on account ofthe fact that the released end of the arm 11 then' drops in front of thepawl, preventing the latter from moving under the arm with the pressureof the spring 18.

The switch can only be reset or reclosed 'by hand; when the bimetalstrip has cooled 05''. This is done by means of a vertical fin geractuated stem 21 mounted in the top of the box 1 and engaging the arm 11between the pivot and contact. A forceful depression of this stemtherefore first causes the contacts to be engaged and then causes thepawl end of the arm to be raised (owing to the spring construction ofthe arm) so that the pawl is freeto-pass under thesame. If the bimetalstrip is still in a heated and warped condition, the pawl cannot moveunder the arm, but if said strip has cooled oil the force of the spring18 will then cause the pawl to move under the arm and hold the same in acontact closing position. This arrangement therefore. as will beevident, prevents the closing of the switch when heat conditions in thecooker are such that a further generation of heat would be damaging tothe food being cooked.

The switch however may be opened. at any time by another vertical fingeractuated stem 22 mounted in the bottom of the box and engaging theextension 19 between the pipe 6 and the back of the box, so as to raisesaid extension and thereby move the pawl clear of the arm 11 regardlessof the setting of the L Strip 20.

From the foregoing description it will be I readily seen that Ihaveproduced such a device as substantially fulfills the objects of theinvention as set forth herein.

While this specification sets forth in detail the present and preferredconstruction of the devlce, still in practice, such deviations from suchdetail may be resorted to as do not form a departure from the spirit ofthe invention, as defined by the appended claims.

Having thus described my invention what ends in a fixed positionrelative to the strip and on one end of which one of the contacts ismounted, spring means acting on the arm to hold the contacts separated,a pivoted pawl whose outer end is adapted to pass under the.

end ofthe arm opposite to the contact to then maintain the'contactsengaged against the resistance of the spring, and an extension formedwith the pawl and engaged by the free end of the bimetal strip, saidextension being positioned so that when moved by the warping of thestrip the pawl will be withdrawn from under the arm.

2. A device as in claim 1, with spring means acting on the pawl to movethe same to an arm-engaging position and of a strength such as to beovercome by the warping of the strip, the end of the arm, when releasedfrom the pawl, projecting in front of and below the outer end of thepawl.

3. A device as in claim 1, with spring means acting on the pawl to movethe same to an arm-eggaging position and of a strength such as to beovercome by the warping of the strip, the end of the. arm when releasedfrom the pawl projecting in front of and below the outer end of thepawl, and a finger-pressed member associated with the arm and engagingthe same in a position to cause the said end of the arm to be raisedabove the outer end of the pawl.

4. A device as in claim 1, in which the arm is of flexible material,with a finger-pressed stem bear-ing down on the arm between its pivotand the contact whereby to cause the pawl engaged end of the arm to beraised to permit the pawl to pass under the same.

